Short arc lamps, in particular xenon high-pressure short arc lamps, have the highest radial intensities per unit area of all known lamps, as well as an arc of very small diameter and very short length. To a good approximation, they are punctiform light sources, and are correspondingly used in projection systems of all kinds, such as film projectors, arc furnaces, photolithography, and in other optical equipment having high radiant intensities per unit area. They include a high-pressure-proof bulb with a spherical or ellipsoid discharge space, for instance of quartz glass; electrodes that as anodes and cathodes are connectable to a source of direct voltage, and comprise tungsten or tungsten with additives; and current ducts fused into the bulb, such as single or multiple molybdenum ribbon ducts or molybdenum cap ducts. Known short arc lamps may include fillings of xenon, mercury, argon, tin or zinc. A mercury lamp requires several minutes to warm up to full operating pressure and light output. This warm-up time is reduced by about 50 percent if xenon at a pressure exceeding one atmosphere is added to the mercury.
From British Patent No. 1,603,699, a short arc lamp of this type filled with xenon and mercury is known. For the electrode spacings in such lamps, which are also known as electrode-stabilized discharge lamps, figures of less than 10 mm to less than 1 mm are given.
A xenon short arc discharge lamp with a bulb of quartz glass and two opposed rod-shaped electrodes is also known from the journal "Illuminating Engineering", Vol. 59, 1964, No. 9, pp. 589-591. The anode has a larger diameter than the cathode; the electrode spacing is shorter than the shaft of the cathode, and the cathode tip is conical.
In the journal "Applied Optics", Vol. 10, 1971, No. 11, pp. 2517-2520, a xenon discharge lamp is described which may contain, in addition to xenon, a doping substance such as thallium iodide.
A xenon short arc discharge lamp is also known from Swiss Patent No. 297 983, in which the electrodes are as close as from 0.5 to 2 mm to one another, so that the positive column of the discharge is suppressed, and the lamp radiates only in the cathode spot. The lamp filling, which is of heavy noble gas (xenon), may have a doping gas having an atomic weight of less than 21 added to it.
In a such a case, the doping merely causes an additional appearance of spectral lines of the doping substance at reduced plasma temperature.